Visual pigments from vertebrate rod and cone cells will be investigated by time-resolved resonance Raman spectroscopy to gain a deeper understanding of the molecular basis of vision and of the role of dipolar excited states in energy tranduction processes. We propose to build a subnanosecond spectrometer to measure the resonance Raman spectrum of rod and cone visual pigments as an explicit function of time following the absorption of a photon, with a time-resolution of 100 picoseconds or better. This technique will provide detailed information about the conformational dynamics of the retinal chromophore in photoreceptor molecules. The sample will be photolyzed by an intense 532 nm light pulse from a mode-locked Nd-YAG laser and its Raman spectrum will be monitored using a delayed probe pulse from a dye laser or harmonic generator. A series of rod and cone pigments including bovine rhodopsin and chicken iodopsin will be studied in this way to provide insight into the initial events in vision: (1) How does the protein component of visual pigments tune the absorption maximum of its retinal chromophore? (2) How does the protein enhance the photosensitivity and channel the photochemistry of its bound retinal? (3) What are the critical light-induced conformational changes in the protein? In particular, the role of the highly dipolar excited state of retinal in the transduction process will be assessed. The resonance Raman spectra of desmethyl retinals, specific isotopic derivatives, and other analogs of retinals, and of visual pigments synthesized from them will be measured to facilitate the interpretation of spectra in definitive structural terms. Resonance Raman studies of these compounds should also contribute to a better understanding of the relationship between the conformation of Vitamin A derivatives (retinoids) and their efficacy in preventing epithelial cancers. The proposed subnanosecond Raman instrument will be valuable for elucidating the conformational dynamics of any system than can be triggered by light (e.g., bacteriorhodopsin and photosynthetic assemblies).